In order to promote adhesion between rubber compositions and synthetic fiber reinforcement, it is known to add various compounds to the rubber and to employ one or more coatings of materials to the fiber which will allow the fiber to become more firmly bonded to the rubber. Present technology has provided various combinations of coatings and additives which may be utilized together to form the article. In such instances, the fiber coating should be capable of bonding to one or more components or active groups present in the rubber stock, particularly the adhesion promoting additives. As noted hereinabove, the present invention is directed toward adhesive active coatings and thus, additives to the rubber stock do not constitute an element of the invention.
Adhesives that are employed in the tire and rubber industries are crosslinked polymeric three dimensional networks. They are used to join two other polymers, i.e., a reinforcing fabric such as cotton, rayon, nylon, polyester or aramid and an elastomer or blend of elastomers. The elastomers are suitably compounded such that the final cured reinforced rubber product will provide an acceptable level of performance.
The principal reinforcements used in rubber products are rayon, nylon, or polyester, alone or in combination with fiberglass, steelcord or aramid. Polyester is presently displaced nylon, cotton and rayon in belt and hose products and is therefore a good candidate for adhesive active coatings. Since 1935, dip systems comprising resorcinol-formaldehyde and rubber latex, or RFL, have been the systems of choice for many reinforced rubber products, with the first commercial application being used in combination with rayon tirecord.
RFL dip systems can be used on polyester but in order to achieve acceptable total performance, modifications are necessary. One such modification is taught by U.S. Pat. No. 3,318,750, which provides an adhesive composition to dip coating fibrous materials for reinforcing vulcanizable rubber. The composition comprises 5 to 50 parts by weight of an aqueous solution and 50 to 95 parts by weight of a rubber latex. The aqueous solution contains 5 to 60 percent by weight of a reaction product of formaldehyde and acetaldehyde with a composition derived from the reaction of triallyl cyanurate and a polyhydric alcohol. The method taught is practiced by applying a finish of aldehyde, unsaturated aliphatic ester of cyanuric acid and a polyhydric alcohol and then a finish of a rubbery latex-resorcinol-formaldehyde dispersion.
This technology was also published in a paper entitled "New Polyester Dip System Results in Improved Adhesion and Processing Costs Reduction" presented to the Division of Rubber Chemistry, ACS, 119th Meeting, Paper No. 23 (1981). It describes a water soluble complex reaction product, called N-3, which contains the cyanurate component set forth in U.S. Pat. No. 3,318,750. Usefulness of the product is attributable to the fact that it provides better adhesion between polyester and rubber than an RFL coating alone. Also it can be used directly with the RFL composition, for a one dip process or, the RFL can be applied thereover in a two dip process.
Another approach has been the coating of polyester fibers with epoxy compounds which may also receive an RFL dip. Adhesion between the cured rubber and the reinforcing cord is thereby improved.
U.S. Pat. No. 4,446,307 provides a stable adhesive composition based upon a polyfunctional epoxide and a catalyst selected from the group consisting of tertiary amines, quaternary ammonium salts, quaternary phosphonium salts and triphenylphosphine. An aqueous solution of the adhesive is applied to the reinforcing filament which is subsequently incorporated into a rubber compound.
U.S. Pat. No. 4,477,497 provides a method of manufacturing polyester fibers having good adhesion to rubber which involves applying an adhesive finish composition to the fiber and then heat treating. The finish comprises a lubricant, an epoxy compound and a novolak resin.
U.S. Pat. No. 4,536,526 also provides a method as well as a finish composition. The latter comprises a lubricant, at least 80 weight percent of which is an ester of triodicarboxylic acid; an epoxy resin and a surfactant. The method calls for the application of the finish to the polyester fiber followed by heat treatment.
Such systems may not have provided satisfactory hydrolytic stability. Also the use of a high heat treatment step to cure the epoxy coating can be deleterious to the heat stabilized reinforcing cord.